Christopher D. Houck of the Bradley/Hasbro Children's Research Center and colleagues at Bradley/Hasbrom, the Rhode Island Hospital, and The Warren Alpert Medical School of Brown University said adolescents who engaged in sexting reported more physical maturity and were more likely to engage in other sexual behaviors.

The study, scheduled to be published in the journal Pediatrics, found 22 percent of at-risk seventh graders participated in sexting, with 17 percent sending texts only and 5 percent sending texts and photos.

The study gathered questionnaire information from 410 teens ages 12 to 14 about whether they had texted or emailed a sexual picture or message within the last six months. They were also asked about their sexual risk behaviors and intentions.

At-risk teenagers who had sexted were four to seven times more likely to engage in a variety of sexual behaviors. Although any sexting appeared to be a marker for sexual risk, sending photos was associated with even greater likelihood of early sexual activity, the study said.